Bone Health Preserved Despite Rapid Weight Loss

by John Gever John Gever,Staff Writer, MedPage Today
September 22, 2008

Action Points

Explain to interested patients that the study found no unhealthy bone loss in patients who lost up to 15% of their body weight in 10 weeks.

Point out that participants were only moderately overweight at baseline and were mainly in their late 30s.

Point out, too, that the diets were monitored more closely than would be likely for most dieters and contained more than the daily recommended allowances for essential vitamins and minerals with calcium intake between 900 and 1,200 mg/day.

Explain that the six-month study could not rule out the possibility of unhealthy bone loss occurring over longer periods.

As overweight adults in their late 30s lost weight on calorie-restricted diets, markers of bone resorption increased, but only to a degree proportionate to the weight loss, reported Leanne Redman, Ph.D., of the Pennington Biomedical Research Center, and colleagues in the Sept. 22 issue of Archives of Internal Medicine.

No changes in bone mineral density or bone mineral content were seen relative to a control group whose weight was maintained at baseline levels, even with a diet that reduced mean weight by nearly 15% in 10 weeks.

"Calorie-restricted interventions did not induce unhealthy changes in total body or hip bone mineral content or density after six months," the researchers wrote.

They said their findings refute the common belief that bones become brittle from rapid, significant weight loss.

The actual mean daily caloric contents of the four diets as prescribed were 2,063, 2,238, 2,091, and 2,873 kcal/day, respectively.

All diets including the control followed the American Heart Association guideline of 30% fat, 15% protein, and 55% carbohydrates as well as supplying recommended levels of all essential vitamins and minerals, including calcium intakes of 900 to 1,200 mg/day.

Participants ate these diets for 24 weeks. For the first 12 and the last two, participants ate only foods prepared by the investigators. From weeks 13 to 22, they selected their own diets based on the caloric targets set by the investigators.

The diets were designed to contain high levels of required nutrients, but participants were told not to take vitamin or mineral supplements, including calcium.

Except for those in the group assigned to a combination of exercise, participants were not to alter their physical activity habits.

Mean weight in the control group was successfully maintained at the baseline level of about 81.5 kg.

The diets that were aimed at inducing 25% caloric deficits -- by diet alone or in combination with exercise -- led to weight losses of 10.4% and 10%, respectively, or about 8 kg (17.6 lb).

The rapid-loss diet led to a loss of about 11 kg (24.25 lb) by week 10, at which point the maintenance diet was begun. The loss from baseline at week 24 was 13.9%.

As expected, most of the lost weight in the three calorie-restriction groups was in the form of fat.

"Compared with the control group, no significant effect of treatment was observed for the changes in bone mineral density and bone mineral content assessed for total body and right hip," Dr. Redman and colleagues reported.

Moreover, these measures did not differ significantly from values predicted on the basis of participants' weight, they said.

In the rapid-loss group, levels of N-telopeptide increased 31% from baseline by the end of the intervention (P<0.001) and osteocalcin increased by 35% (P not given).

However, the changes in serum markers did not correlate significantly with bone mass measurements.

There were also no significant differences in study outcomes by gender.

In an interview, Dr. Redman acknowledged that the diets were more closely supervised than is possible for real-life dieters in the community.

"Yet if you look at the kind of dieting that people undertake, a 20% to 25% calorie restriction is fairly typical of what people would do in a free-living situation," she added.

She said that the diets in the study would work out to 2,200 kcal/day for an average 180-pound, 28-year-old man, "which is definitely feasible for the general population to adhere to," she said.

The researchers said that additional research is needed over longer periods and including evaluations of bone architecture "to ensure that bone quality is preserved with weight loss."

One potential limitation of the study pointed out by the authors in the interpretation of the findings is "the capability of dual-energy x-ray absorptiometry to detect changes in bone over six months, especially when body weight is drastically changing."

However, they wrote, "importantly, there are published studies that have observed changes in BMD and/or BMC with similar interventions that have been shorter than six months."

External funding for the study came from National Health and Medical Research Council of Australia.

No potential conflicts of interest were reported.

Reviewed by Zalman S. Agus, MD Emeritus Professor University of Pennsylvania School of Medicine

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